Dead wood is a key substrate of forests that plays an important role in fertility and productivity. However, dead wood is scarce in traditionally managed forests like Mediterranean dehesas. The chemical composition of downed dead wood in Quercus pyrenaica dehesas was analysed in different physical decomposition stages as a proxy of dead wood decay length. We also assessed the contribution of fungal activity, by quantifying ergosterol, to the chemical composition of deadwood. Chemical analyses included elemental composition determination, thermogravimetry and infrared spectroscopy. Our results showed that both the physical decomposition stage and ergosterol content extensively predicted the chemical composition of Q. pyrenaica dead wood decay processes under field conditions. The physical stage was a better predictor of the C/P ratio and polysaccharides proportion, while ergosterol better predicted P content and the N/P ratio. In other cases like lignin, the relation between ergosterol content and chemical composition varied depending on the physical stage. In addition, environmental local factors differentially affected chemical composition across physical decomposition stages. We conclude that the physical decomposition stage and ergosterol content complementarily contribute to estimate the temporal behaviour of the chemical composition of dead wood in Mediterranean areas. Moreover, we recommend using the FT-IR analysis to assess the nature of temporal chemical changes in downed dead wood. Finally, our study claims to consider the potential impact of local environmental factors, such as air temperature and relative humidity, on dead wood decay processes in traditionally managed forests in the current global change scenario., Financial support was provided by the Spanish Ministerio de Economía y Competitividad (CGL2016-78181-R). JQ was supported by Spanish Ministry of Science and Innovation, project PID2020-115140RB-I00/AEI/https://doi.org/10.13039/501100011033.

17 páginas; 7 figuras y 1 tabla; Functional databases can be consulted in the Institutional Repository of the University of Alicante (RUA); The online version contains supplementary material available at http://doi.org/10.1007/s10841-026-00769-w, Despite growing research on insect decline, long-term temporal analyses integrating functional approaches remain scarce. Understanding how functional traits relate to temporal changes in community composition is particularly important for saproxylic communities, which are highly sensitive to forest environmental changes. In this study, we analysed interannual and spatial changes in the taxonomic and functional dimensions of saproxylic beetle and spider communities inhabiting tree hollows across three Mediterranean forest types (riparian ash forest, deciduous oak forest and sclerophyllous oak woodland). Specimens were sampled monthly using emergence traps during two complete years separated by an 11-year period. We assessed variation in species richness, functional diversity (functional richness and divergence), and functional structure. We also explored whether species-level temporal changes in relative abundance were associated with species’ positions in functional trait space. Beetle and spider species richness differed among forest types and between sampling periods, whereas functional richness varied mainly spatially. Trait-associated shifts in species relative contribution were not consistent across taxa or forests. The clearest trait-associated changes in relative abundance were detected in wood-dependent beetles (saprophagous, saproxylophagous and xylophagous) from Quercus pyrenaica forests, where larger and less dispersive species showed lower relative abundance in the second sampling period. In contrast, there was little evidence of consistent trait-mediated changes in spider assemblages over time. Overall, our results indicate that temporal functional responses of saproxylic arthropod communities are context dependent, varying across forest types and trophic guilds and suggest maintaining structurally complex forests and continuous networks of suitable tree hollows to buffer these communities under ongoing environmental change, specially in Q. pyrenaica forests. Implications for conservation The present study remarks the importance of integrating functional and taxonomic approaches to provide a more comprehensive understanding of observed community changes at a spatio-temporal scale, helping us to infer which forests may be more vulnerable under ongoing environmental change., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Financial support was provided by Grants CGL2009-09656 and PID2020-115140RB-I00 funded by MCIN/AEI/https://doi.org/10.13039/501100011033 and grant CIAICO/2022/177 funded by Generalitat Valenciana (Conselleria de Educación, Cultura, Universidades y Empleo). CPC received funding from the Estonian Research Agency (PRG2142). JQ grant is co-financed by the European Social Fund Plus and the Operational Program of the Regional Government of Castilla y León and the Consejería de Educación.

[EN] Forests of the Mediterranean Basin provide a wide range of provisioning and regulating services that are currently jeopardised by land-use change. Although many ecosystem services are mediated by insects, most of the studies that have focused on how to enhance diversity in traditionally managed forests are about plants and
vertebrates. Quercus pyrenaica woodlands of the Western Iberian Peninsula constitute a scenario in which traditional human practices (i.e., extensive livestock grazing, pollarding, firewood, forest thinning, etc.), and their progressive abandonment, have generated differences in landscape that affect habitat and microhabitat
structures. We used saproxylic beetles (deadwood-dependent species) as biological indicators because they are the most diverse taxa and provide important ecosystem services related to deadwood decomposition, forest pest control and pollination. We modelled the response of two taxonomic (species richness and abundance), one
ecological (species diversity of order 1) and two functional (functional richness and redundancy) diversity metrics to the environmental variables that result from traditional management or its abandonment at habitat and microhabitat levels. We included 16 explanatory variables related to forest structure, tree microhabitats and abiotic factors, which were grouped into eight principal components. Linear regression was the best fitting model
for data. The resulting models were used to perform diversity predictions in different scenarios. We found that abandonment of some traditional forest management activities in the Mediterranean Region reduced taxonomic saproxylic beetle diversity, which may be further aggravated by climate change. We suggest minimal management actions to improve taxonomic and ecological saproxylic beetle diversity related to habitat and tree management (i.e., maintenance of >20% scrub coverage, >20 m3/ha of deadwood on soil and >20 hollow trees/ha).
However, actions that boost saproxylic biodiversity do not ensure the community¿s higher functional resilience. We should also promote tree microhabitat diversity to reduce the vulnerability of saproxylic beetle functions to environmental changes., Financial support was provided by the Ministerio de Economia y Competitividad (Projects CGL2016-78181-R) and Ministerio de Ciencia e Innovacion (PID2020-115140RB-I00) granted to EM and EG. This research forms part of Sandra Martinez Perez's PhD studies granted by 'Ministerio de Economia, Industria y Competitividad' (BES-2017-080278).